1. Field of the Invention
The present invention relates to a zoom lens and a information device. A zoom lens according to the invention can be suitably used for a digital camera, and also, be used for a camcorder or a silver salt camera. An information device according to the invention can be embodied as a digital camera, a camcorder, a silver salt camera, etc., and further, be embodied as a portable information terminal device.
2. Description of Related Art
Nowadays the market for digital cameras has expanded and users have various demands for digital cameras. The users always desire enhancement of quality of photographed images and miniaturization of a main body of a digital camera. Thus, compatibility of improvement in performance and miniaturization is also desired for a zoom lens used as a photographing lens.
In order to accomplish the miniaturization of a zoom lens, it is necessary to shorten an overall length of lenses when in use (i.e., a distance from a lens surface which is nearest to an object side to an image plane), and also it is important to reduce thickness of each group of lenses to curb the overall length at the time of storage.
In order to accomplish the improvement in performance, in light of resolving power it is necessary to secure resolving power corresponding to an imaging device having the number of pixels of at least four million, or preferably, pixels of eight million or over.
Additionally, there are a number of users who desire widening of a field angle of the photographing lens, so that it is desirable to provide a half field angle of a wide-angle position of the zoom lens to be more than 38 degrees. The half field angle having 38 degrees is equivalent to a focal length of 28 mm in terms of a 35 mm silver salt camera using a 35 mm size (so-called Leica size) silver salt film.
Furthermore, it has been desired that magnification power is as large as possible. It is considered to be possible to deal with most of the general photographing if a zoom lens has a focal length of worth 28 mm to 135 mm in terms of 35 mm silver camera (i.e., approximately 4.8 times magnification power).
Conventionally, as a zoom lens consisting of four groups of lenses there is disclosed in Japanese Patent Laid-Open No. 04-190211 (“Reference 1”) a zoom lens including a first group of lenses having positive refractive power, a second group of lenses having negative refractive power, an aperture stop, a third group of lenses having positive refractive power and a fourth group of lenses having positive refractive power which are subsequently arranged from an object side to an image side, wherein during a change in magnification power carried out from a wide-angle position to a telephoto position, the first group of lenses and the third group of lenses move monotonously to the object side, the second group of lenses remains unmoved and the fourth group of lenses moves.
In Japanese Patent Laid-Open No. 04-296809 (“Reference 2”) there is also disclosed a zoom lens having the four-group structure as described above, wherein during a change in magnification power carried out from a wide-angle position to a telephoto position the first group of lenses and the third group lenses move monotonously to the object side, the second group of lenses moves monotonously to the image side and the fourth group of the lenses moves.
In Japanese Patent Laid-Open Nos. 2003-315676, 2004-212616, 2004-212618 and 2004-226645 (“Reference 3–6”, respectively) there is also disclosed a zoom lens having the four-group structure as described above, wherein during a change in magnification power carried out from a wide-angle position to a telephoto position the first group of lenses and the third group of lenses move monotonously to the object side and the second group of lenses moves toward the object side after the second group of lenses once moves toward the image side.
According to the zoom lenses disclosed in the References 1 and 2 a half field angle of a wide-angle position of the zoom lenses falls within about 25 to 32 degrees. In the References 3 to 6 a zoom lens having a half field angle of a wide-angle position of the zoom lens which falls within 34 to 37 degrees is proposed. However, the magnification power of such zoom lens is up to four-odd times.